Photosensitive films comprising silver halides have been a primary object of photographic research. Although the photolytic reduction of halides to provide the latent silver photographic image is of major interest, the reverse reaction through which metallic silver is reconverted to a silver halide by the action of light or heat has also been the subject of study.
An early discussion of the changes in absorption behavior produced in a darkened photographic plate by exposure to red light is provided by Cameron and Taylor in Photophysical Changes in Silver-Silver Chloride Systems, Journal of the Optical Society of America, Volume 24, pages 316-330 (1934). These authors verified that optically or chemically darkened silver halide-containing emulsions can be selectively bleached, particularly with red light, such that they become more transparent to light of the bleaching wavelength. This behavior is referred to as color adaptation. It was further noted that polarized bleaching light produced a dichroic, birefringent image in the darkened film.
Optically-induced dichroism has also been observed in polycrystalline silver halide layers produced by evaporation techniques. Enhanced dichroism in silver halide films containing additions of vacuum-evaporated silver was reported by V. P. Cherkashin in Soviet Physics--Solid State, Volume 13, Number 1, pages 264-265 (1971).
It has been postulated that the anisotropic absorption behavior of silver halide films is due to enlongated metallic silver colloids. This hypothesis is not inconsistent with certain absorption characteristics which have been observed for granular metal films. The optical properties of some sputtered gold and silver island films are described by R. H. Doremus in J. Chem. Phys., Volume 42, pages 414-417 (1964), by R. W. Cohen et al., in Physical Review B, Volume 8, Number 8, pages 3689-3701 (1973), and in other papers.